SUFC

TgSUFC is an ATPase component of the plastidic SUF (sulfur utilization factor) iron-sulfur cluster biogenesis pathway operating in the apicoplast of Toxoplasma gondii, and it is essential for parasite division and membrane homeostasis (PMID:35810787). Conditional depletion of TgSUFC causes severe, irreversible defects in parasite division and membrane integrity, establishing its requirement for iron-sulfur cluster assembly (PMID:35810787). Because Fe-S cofactors feed downstream apicoplast metabolism, loss of TgSUFC impairs apicoplast-generated fatty acid synthesis, though exogenous fatty acid supplementation does not fully rescue growth, indicating fatty acid deficiency is not the sole lethal consequence (PMID:35810787). TgSUFC depletion also disrupts apicoplast-derived isoprenoid biosynthesis, producing downstream defects in GPI-anchored protein targeting and parasite motility, and thereby placing the SUF pathway upstream of multiple isoprenoid-dependent processes (PMID:35810787). Beyond these loss-of-function phenotypes, no structural, enzymatic, or interaction-level detail of TgSUFC has been characterized in the available corpus.

1. 2022 Medium

   Establishing whether the apicoplast SUF pathway is essential in Toxoplasma required a component-level test; conditional depletion of the ATPase subunit TgSUFC showed the pathway is indispensable for parasite division and membrane homeostasis.

   Evidence Conditional knockdown/depletion mutant with division and membrane homeostasis phenotyping in T. gondii

   PMID:35810787

   Open questions at the time

   • No biochemical demonstration of TgSUFC ATPase activity or Fe-S cluster assembly in vitro
   • Direct interaction partners within the SUF machinery not mapped
   • No structural model of the TgSUFC subunit or complex
2. 2022 Medium

   To identify which downstream apicoplast function is compromised, lipid analysis and rescue experiments showed TgSUFC loss impairs fatty acid synthesis but that this deficiency alone does not explain lethality.

   Evidence Lipid/fatty acid analysis with exogenous fatty acid supplementation rescue in T. gondii

   PMID:35810787

   Open questions at the time

   • The additional lethal consequences beyond fatty acid deficiency remain unresolved
   • Which specific Fe-S-dependent enzymes are inactivated is not defined
3. 2022 Medium

   To connect Fe-S biogenesis to broader parasite biology, phenotypic assays showed TgSUFC depletion disrupts apicoplast-derived isoprenoid biosynthesis, causing defects in GPI-anchored protein targeting and motility.

   Evidence Conditional knockdown with GPI-anchored protein localization and motility assays in T. gondii

   PMID:35810787

   Open questions at the time

   • The specific isoprenoid-dependent enzyme(s) requiring Fe-S clusters are not identified
   • Causal chain from isoprenoid loss to GPI mistargeting not mechanistically dissected

• The biochemical activity of TgSUFC, its assembly into the SUF complex, and the direct Fe-S client enzymes that link the pathway to fatty acid and isoprenoid metabolism remain uncharacterized.
• No in vitro reconstitution of TgSUFC ATPase or Fe-S cluster transfer activity
• No structural or interaction data for the T. gondii SUF machinery
• Identity of Fe-S-dependent target enzymes not established